Numerical modelling for intergranular corrosion of stainless steel based on microscopic analysis of corroded texture

Yamamoto, Masahiro ; Igarashi, Takahiro  ; Komatsu, Atsushi ; Motooka, Takafumi; Ueno, Fumiyoshi  

Intergranular corrosion occurred in stainless steels in nitric acid solution at a spent fuel reprocessing plant. Several reports introduced that intergranular corrosion affected by the impurity elements. We analyzed the initial stages of intergranular corrosion microscopically and attempted to simulate them numerically. The specially prepared 25Cr-20Ni stainless steel which was include only phosphorus for an impurity element was used for analyzing the initial stage of intergranular corrosion. Phosphorus segregated into grain boundary using various thermal treatments. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. The ratio increased with higher phosphorus segregation by thermal treatment. These values were used for numerical simulation of intergranular corrosion. The cross sectional images calculated by the simulation were very good agreement to the actual observations.